Role of Meprin A in acute kidney injury Gur P. Kaushal, Ph.D. Project Summary Meprin A, a membrane-associated neutral metalloendoprotease, is highly expressed at the brush- border membranes of proximal tubules in the corticomedullary junction. The specific role of meprin A during acute kidney injury (AKI) is not fully understood. Our studies identified that meprin A is the major matrix-degrading protease in the rat kidney cortex capable of degrading the extracellular matrix (ECM) proteins including collagen IV, fibronectin, laminin, and nidogen in vitro. Our recently published and preliminary studies demonstrated that meprins are also capable of producing biologically active proinflammatory cytokine interleukin 1- from its inactive proform and proteolytically processing chemotactic cytokine MCP-1, suggesting that meprins are also important in inflammation. Following ischemia-reperfusion (IR)- and cisplatin-induced AKI, meprin A is redistributed throughout the cytoplasm and extracellularly adhering toward the basolateral plasma membrane and the cleaved form of meprin A is excreted in the urine during AKI. These studies suggest that shedding and altered localization of meprin A in places other than the apical brush-border membranes may be deleterious in vivo in acute tubular injury. How membrane-associated meprin A is redistributed and shed is not known. Preliminary studies suggest that meprin A shedding may involve a member of the ADAM (a disintegrin and metalloproteinase) family. Using in vivo models of cisplatin- and IR-induced AKI, we demonstrated that actinonin, a potent inhibitor of meprin A inhibits meprin A in vivo and ameliorates acute kidney injury and meprin A-deficient C3H/He mice are resistant to AKI. Interestingly, we observed that nidogen and meprin-beta fragments, undetectable in the urine of normal mice, increased significantly before the rise in serum creatinine during the progression of IR- and cisplatin- induced AKI. Thus, a unique opportunity exists to further explore the role and mechanism of action of meprin A in AKI. We hypothesize that meprin A, with its enormous destructive potential, is detrimental to renal proximal tubules due to altered localization during AKI and that understanding its mechanism of action is important in protecting or reducing AKI. In addition, we hypothesize that meprin and nidogen fragments excreted during AKI will serve as important biomarkers for early detection of AKI. We will test these hypotheses through the following specific aims: 1. Examine the temporal relationship between meprin A redistribution, renal injury, leukocyte infiltration, meprin A shedding, and urinary excretion of meprin subunits during AKI using experimental models of IR and cisplatin nephrotoxicity. 2. Examine meprin A-mediated in vivo degradation products of nidogen during IR and cisplatin nephrotoxicity. 3. Determine the mechanisms of meprin A-mediated inflammatory effects and functional significance of meprin A inhibition after the onset of AKI. Understanding the underlying role of meprin A in AKI will provide insights for specific therapeutic interventions to prevent acute kidney injury.